In recent years, in automotive industry, developing a vehicle body structure capable of reducing injury to passengers in collision is an urgent issue. A vehicle body structure excelling in such collision safety can be achieved by absorbing impact energy in the event of collision by structural members other than the passenger compartment, so as to minimize deformation of the passenger compartment and secure a survival space.
That is, it is important to enable the structural members to absorb impact energy. To improve absorption of impact energy, it is crucial to stabilize a buckling mode and to prohibit bending or fracture in the middle, and it is necessary to accurately evaluate what degree of fracture risk has been reached at the present moment.
However, in a collision or stamping of an automobile, each member goes through a complicated deformation path, and thus the fracture risk varies depending on its deformation history. Therefore, it has been difficult to accurately evaluate the fracture risk per portion of each member.
There have conventionally been many proposals of methods and apparatuses and the like for predicting a fracture. For example, Japanese Laid-open Patent Publication No. 2007-152407 (Patent Document 1 below) discloses an arithmetic processing apparatus which predicts a fracture in stamping by using a stamping simulation means, an equivalent plastic strain calculation means, a formation crack determination value calculation means, and a formation crack determination means. The formation crack determination means of the arithmetic processing apparatus is capable of predicting a formation crack more accurately when predicting a formation crack with reference to a formation limit diagram by predicting a formation crack by whether or not a determination target equivalent plastic strain exceeds a formation crack determination value in the proceeding direction of the strain. However, the method of Patent Document 1 is to evaluate a fracture margin by the distance to a non-proportional formation limit value in a strain space, and the method needs to recalculate the non-proportional formation limit value every time the proceeding direction of the strain changes, and hence is complicated.
Further, Japanese Laid-open Patent Publication No. 2007-232714 (Patent Document 2 below) discloses that, with a line obtained by converting a hole expanding ratio into a stress being taken as a fracture limit stress line, the fracture risk of a material is quantitatively evaluated by comparing the relation between data obtained from a numerical analysis using a finite element method and the fracture limit stress line. In the method of Patent Document 2, it is possible to easily and efficiently obtain a fracture limit line when determining the fracture limit of a thin sheet in a process including one or more deformation path variations, and determine a fracture limit with high prediction accuracy.
Further, Japanese Laid-open Patent Publication No. 2007-232715 (Patent Document 3 below) discloses that, with a line obtained by converting a hole expanding ratio into a stress being taken as a fracture limit stress line, the fracture risk of a material is quantitatively evaluated by comparing the relation between data obtained from a numerical analysis using a finite element method and the fracture limit stress line. In the method of Patent Document 3, it is possible to easily and efficiently obtain a fracture limit line when determining the fracture limit of a stretch flange part in a thin sheet in a process including one or more deformation path variations, and determine a fracture with high accuracy, thereby allowing evaluation of the risk of fracture during stamping or in the event of collision.
Moreover, Japanese Laid-open Patent Publication No. 2007-285832 (Patent Document 4 below) discloses a fracture limit obtaining system in which a user terminal provides material data as the target of fracture determination to a server and obtain data of a fracture limit line from the server. It discloses that the user terminal quantitatively evaluates the fracture risk of a material using the obtained fracture limit line.